1. Field of the Invention
The present invention generally relates to a data transmitting apparatus, a data receiving apparatus, and a data communication system.
2. Description of the Related Art
An increasing number of methods have been used to realize communication in familiar surroundings along with the development of the information society, and the communication speed has remarkably increased. To further increase the communication speed, an acceptable use policy is set for a new medium. In most types of existing wireless communication, a regulation requires that a certain bandwidth should be used only for a predetermined application. However, some of the bandwidths can be used for a plurality of applications. Furthermore, very wide bands laid over plurality of other applications' bands are determined to be opened for Ultra Wideband (UWB) communication, with a condition of limiting use for low-power short-range communication. In this case, however, a wireless communication for an application has a possibility of interfering with a wireless communication for another application.
The regulation for the UWB obliges that, if a system licensed to use a frequency is not very resistant to interference waves, UWB systems should stop transmission when it detects a radio wave from the licensed system. This technology is referred to as a Detect And Avoid (DAA). A concept of the DAA is understood to be covered by a concept of cognitive wireless communication. The cognitive wireless communication is a technology of performing sensing, recognizing, and getting adapted for an environment when communicating. If the object to be recognized is the use of frequencies nearby and the adaptation condition is to stop the transmission upon detecting the transmission from the licensed system, the definition of cognitive radio is equivalent to the DAA. Although this technology is necessary to protect the licensed system, a sudden transmission stoppage affects communication performance of the UWB and the cognitive system.
If only a part of a packet is not transmitted due to the transmission stoppage, the data can be recovered by error correction and retransmission control that most of wireless communication systems have the functions. However, the retransmission uses a bandwidth for a normal traffic, which reduces throughput. Therefore, various technologies have been proposed to reduce the amount of the retransmission in a system that performs both of the error correction and the retransmission control.
For example, JP-A 2005-269480 (KOKAI) discloses a technology used by a system that transmits transmission data, in which frame data to be transmitted are coded with an outer error-correcting code, divided into a predetermined number of blocks, and coded with an inner error-correcting code. The technology is to determine whether to perform the retransmission based on likelihood after decoding received transmission data with the inner code. The system requests the retransmission block by block if a frame is estimated to include so many errors according to the inner code that cannot be corrected by the outer code, whereby increasing transmission efficiency.
However, according to the technology disclosed in JP-A 2005-269480 (KOKAI), because relation between each of the divided blocks and the frame is not known at the time of decoding the inner code, the system may request the retransmission of the block of the frame that is not allowed to be retransmitted. As a result, the transmission efficiency can be reduced.
Moreover, according to an aspect of the cognitive communication and the DAA, the system stops the transmission at the frequency immediately after the detection of the transmission from the licensed system. Therefore, the errors burst in a different manner from the errors caused by fad. In such a case, the amount of the retransmission can be reduced by retransmitting only the bursting errors; however, the technology disclosed in JP-A 2005-269480 (KOKAI) also retransmits blocks with non-burst errors such as errored block due to fading, resulting in reduced transmission efficiency.